May skip this slide quickly: not mention data model.Several popular tools that are used widely by Earth Science community.

The shared dimensions can be easily used by Earth Science applications to specify the coordinate variables.

Group hierarchy and User-defined datatypes are key concepts to addTo the enhanced model.After this slide, ask the audiences how many people heard of CF conventions, how many people would like to know how CF attributes can affectthe visualization results.

May quickly go through this slide if audiences know CF attributes._FillVaule only specifies one distinct missing or undefined value. Using valid_min, valid_max or valid_range multiple distinct missing or undefined values can be filtered out

Be careful when using these two attributes. Joe will share with you MODIS examples.

Also make sure to use the exact format. Some tools are picky.

At the end of slides, just mention other CF requirement: The variable and attribute names can only have number, letter and underscore. No other characters are allowed.

Demos:_FillValue: 1) Use HDFView to show the data, 2) IDV first shows the data without the fillvalue attribute 3) Add _FillValue attribute at HDFView. Change the HDF5 dataset name to another name.4) Save the file(not to another HDF5 file) 5) Open with the IDV again, this time the _FillValue is not printed.

Demos:_FillValue: 1) Use HDFView to show the data, 2) IDV first shows the data without the fillvalue attribute 3) Add _FillValue attribute at HDFView. Change the HDF5 dataset name to another name.4) Save the file(not to another HDF5 file) 5) Open with the IDV again, this time the _FillValue is not printed.

Demos:Show the scale factor and add_offset. The initial value and the final value.2.Show the wrong attribute name and the right attribute name3.. Demo:file with the wrong attribute names(1,2,3…)file with the right attribute names(1010,1020, etc.)

Demos:Show the scale factor and add_offset. The initial value and the final value.2.Show the wrong attribute name and the right attribute name3.. Demo:file with the wrong attribute names(1,2,3…)file with the right attribute names(1010,1020, etc.)

Demos:Screenshots:Let the audience note the “coordinates” attribute.4. Show IDV, don’t display the value plot(IDV has a bug), just show the vertical coordinate

Demos:Screenshots:Let the audience note the “coordinates” attribute.4. Show IDV, don’t display the value plot(IDV has a bug), just show the vertical coordinate

The netCDF-4 requires the association of dimensions with coordinate variables.

Transcript of "Interoperability with netCDF-4 - Experience with NPP and HDF-EOS5 products"

9.
• In this tutorial, we only review the key CF
attributes that affect the access of NASA and
other Earth Science HDF and HDF-EOS data
via popular visualization tools.
Apr. 17-19, 2012
HDF/HDF-EOS Workshop XV
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www.hdfgroup.org

10.
Key CF data description attributes
Attribute
Description
Units
A string that represents the quantity of measurement. A
variable with no units attribute is assumed to be
dimensionless.
long_name
A descriptive name that indicates a variable‟s content.
standard_name
A standard name that references a description of a
variable‟s content in the standard name table of CF
conventions.
_FillValue
A value used to represent missing or undefined data.
valid_min
Smallest valid value of a variable.
valid_max
Largest valid value of a variable.
valid_range
Smallest and largest valid values of a variable.
Use these attributes if possible, especially use
_FillValue, valid_min,valid_max if you have missing value(s).
Apr. 17-19, 2012
HDF/HDF-EOS Workshop XV
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11.
Reduction of dataset size
Attribute
Description
scale_factor
If present for a variable, the data are to be multiplied by this
factor after the data are read by an application.
add_offset
If present for a variable, this number is to be added to the data
after it is read by an application. If both scale_factor and
add_offset attributes are present, the data are first scaled before
the offset is added.
The equation that describes the usage of scale_factor and add_offset is:
Final_data_value = “scale_factor” * Raw_data_value + “add_offset”;
Apr. 17-19, 2012
HDF/HDF-EOS Workshop XV
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22.
• We will use several demos to show the
differences for the last two cases
• netCDF(classic) HDF5
• netCDF(classic) CF HDF5
• ncdump can dump all demo files
Apr. 17-19, 2012
HDF/HDF-EOS Workshop XV
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36.
An HDF-EOS5 file structure
HDFEOS
GRIDS
CloudFractionAndPressure
Data Fields
CloudFraction
CloudPressure
Because of the group hierarchy, we can only augment the
HDF-EOS5 file by following the netCDF enhanced model
Apr. 17-19, 2012
HDF/HDF-EOS Workshop XV
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37.
An example: Augment an HDF-EOS5 Grid
• The HDF-EOS5 saves the
coordinate information
XDim and YDim in an
equation
HDFEOS
GRIDS
• The tool retrieves the
CloudFractionAndPressure
values of XDim and YDim
Data Fields
CloudFraction[XDim][YDim]
• It creates coordinate
CloudPressure[XDim][YDim]
variables XDim and YDim
XDim
with the raw values
YDim
• Then it associates the
coordinate variables with
the data variables
• Then netCDF-4 can follow
the netCDF enhanced
model to access the HDFEOS5 data
www.hdfgroup.org

57.
Acknowledgements
This work was supported by Subcontract number
114820 under Raytheon Contract number
NNG10HP02C, funded by the National Aeronautics
and Space Administration (NASA) and by
cooperative agreement number NNX08AO77A from
the NASA. Any opinions, findings, conclusions, or
recommendations expressed in this material are
those of the authors and do not necessarily reflect
the views of Raytheon or the National Aeronautics
and Space Administration.
Apr. 17-19, 2012
HDF/HDF-EOS Workshop XV
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